In an internal combustion engine, it is known that when the air to be suctioned into a combustion chamber flows through an intake passage, a so-called pulsation occurs in the air. In the case where the exhaust gas discharged from the combustion chamber to the exhaust passage is introduced into the intake passage, the pulsation occurring in the air flowing through the intake passage becomes large.
In the case where the pulsation occurs in the air flowing through the intake passage, the air flow direction changes between the forward direction (i.e. the direction toward the combustion chamber) and the backward direction (i.e. the direction opposite to the forward direction). Recently, for example, in order to decrease emissions discharged from the engine, it is desired that the flow rate of the air flowing through the intake passage in the backward direction as well as that in the forward direction are detected.
A flow rate detection device for detecting the flow rate of the fluid flowing in the backward direction as well as that in the forward direction is described in the Patent Document 1. This device is a so-called silicon chip type flow rate measurement device and has a heating resistor and two temperature detectors. One of the detectors detects the temperature of the air coming thereto (hereinafter, this detector will be referred to as—fluid temperature detector—) and the other detector detects the temperature of the heating resistor (hereinafter, this detector will be referred to as—heating resistor temperature detector—). In this device, the temperature higher than the fluid temperature detected by the fluid temperature detector by a constant temperature is set as a base temperature, it can be judged if the fluid passing through the device flows in the forward or backward direction on the basis of the relationship between the base temperature and the heating resistor temperature detected by the heating resistor temperature detector and the flow rate of the air passing through the device can be measured on the basis of the difference between the base temperature and the heating resistor temperature detected by the heating resistor temperature detector.
Therefore, if the device described in the Patent Document 1 is positioned in the intake passage of the engine, the flow rate of the air flowing through the intake passage in the backward direction as well as that in the forward direction can be detected.